The present invention relates to self-cleaning ovens and in particular, to a system for controlling the operation of a self-cleaning oven.
During the use of an oven of an electric or gas range, deposits will generally accumulate as a result of spills, boil overs and other unintended release of foods from their cooking containers. In order to ease the cleaning of the spillage, provision is made in some ranges, known as xe2x80x9cself-cleaningxe2x80x9d ranges, to raise the temperature of the cooking cavity well above that which would be used in cooking in order to carbonize or burn out the residue. In general, this is achieved by the selection through the range""s controls of a self-clean cycle. Initiation of this cycle typically sets a high control temperature for the range, locks the oven door at some predetermined time or temperature and proceeds to heat the cavity to a relatively high temperature for a predetermined time before ending the cycle, allowing cooling to occur and then releasing the door lock as an end to the cycle.
Typically, the time period set for this self-clean cycle is determined by the assumption of a worst case cycle. During the cycle, odors or even smoke may be released in the range environment and significant energy is used to hold the cooking cavity at a high temperature. Because of odor and smoke release, users are advised to open windows and will frequently leave the kitchen area for an extended period of time while self-clean is performed.
If a method can be devised which adjusts the time of self-cleaning to that needed for the existing degree of soil accumulation, then cycle times and their negative impact on kitchen enviromnent and energy usage can be minimized.
U.S. Pat. No. 4,954,694 discloses a self-cleaning oven which incorporates a heat controlled unit which is responsive to a gas signal from a gas sensor located in the exhaust passage. The gas sensor measures humidity or carbon dioxide levels. The heat control samples the gas signal at a given time interval to detect a variation of amount of the gas component and detect a first inflection point from decreasing to increasing or visa versa in a gas-component variation and a second inflection point from decreasing to increasing or vice versa in the gas component variation after detection of the first inflection point. The heat control means determines the heating time period for cleaning in correspondence with the second inflection point. An oxidizing catalyst is provided in the exhaust passage, upstream of the gas sensor.
It is generally recognized that the combustion of food product will generate various gases or gas components. This invention is generally directed to controlling the operation of a self cleaning oven wherein the duration of a self clean cycle wherein foods are combusted is controlled by monitoring the xe2x80x9csignaturexe2x80x9d response of gas components resulting from the combustion of food soils in an oven cavity. More particularly, the time period of the self clean cycle is responsive to the amount of soil accumulation in the oven.
The present invention controls the duration of a self-clean cycle by monitoring a gas component produced by food combustion and by determining a rate of change between successive gas component signals. Termination of the self clean cycle is initiated once the determined rate of change is maintained below a minimum preset rate of change value for a predetermined length of time. The self clean cycle may be terminated, for example, a predetermined time after the rate of change is maintained below a minimum preset rate of change value for a predetermined length of time. In one embodiment, the measured gas component may be carbon monoxide.
The present invention includes a gas sensor or sensor mechanism to detect gas concentrations found in the exhaust gas during a self cleaning operation. The gas sensor is located remote from the oven and remote from the flue passage, but in communication therewith through a flue gas delivery system. This system comprises a relatively small diameter outlet tube or tubing which branches off from the main flue gas passage and which delivers flue gases to the sensor mechanism. A valve may be optionally provided on the inlet to the small diameter tubing to limit the gas sensor""s exposure to flue gases.
In order for the user of the range to be made aware of the status of the self-cleaning cycle, a display may be provided. During the initial evaluation period, while the control is determining the extent of cleaning required, an icon, such as an hour glass, can be displayed on an electronic display located on the range console to symbolize that the clean cycle is in process. Once the self-cleaning duration is determined by the control system, a count down timer can be displayed in lieu of the icon, indicating to the user the time remaining for the completion of the cleaning cycle.
In a further embodiment, the present invention may include an alternate method for determining the amount of clean time needed to perform the self-cleaning cycle wherein the number or length of bake and broil cycles the user has performed since the last self-clean cycle is counted. The number of days since a self-clean cycle has been run is also counted. A minimum clean base time based on these factors could then be determined. Thus, when the user selects and starts a clean cycle, the number or length of bake and broil cycles and the number of days the oven has not been cleaned, are retrieved and used to determine the appropriate clean time. The calculated clean time is displayed to the user to show the length of the clean cycle. This method could be used in lieu of using a gas sensor, or as a back up method in the event of sensor malfunction.